Recombinant attenuation of porcine reproductive and respiratory syndrome (PRRSV)

ABSTRACT

The present invention relates to live PRRS viruses which are attenuated by amino acid mutations in a specific site of the viral protein coded by the open reading frame (ORF) selected from the group of ORF  1   a , ORF  1   b  and/or ORF  2 . The invention also pertains to nucleotide sequences coding said viruses, methods of generating such viruses and their use for the preparation of a pharmaceutical composition for the prophylaxis and treatment of PRRS infections.

RELATED APPLICATIONS

[0001] This application claims benefit of prior U.S. application Ser. No. 09/772,316, filed Jan. 26, 2001 which claims benefit of prior provisional application Serial Nos. 60/181575, 60/181605, and 60/181606, all filed Feb. 10, 2000, the disclosures of all of which are incorporated by reference in their entirety.

FIELD OF THE INVENTION

[0002] The present invention relates to live PRRS viruses which are attenuated by amino acid mutations on specific sites of the viral protein coded by the open reading frame (ORF) selected from the group of ORF 1 a , ORF 1 b and/or ORF 2. The invention also pertains to nucleotide sequences coding said viruses, methods of generating such viruses and their use for the preparation of a pharmaceutical composition for the prophylaxis and treatment of PRRS infections.

BACKGROUND OF THE INVENTION

[0003] Mystery swine disease, later renamed porcine reproductive and respiratory syndrome (PRRS), is caused by an enveloped positive-stranded RNA virus of the family arteriviridae (Snijder E. J. and J. J. M. Meulenberg, 1998, J. Gen. Virol. 79(5):961-971). About 10 to 15 years ago, two different PRRS virus strains emerged apparently independently in the USA and Europe. The disease is now endemic in many swine producing countries in North America, Europe and Asia. It continues to be a major cause of reproductive loss and respiratory disease in swine. In the USA the prevalence of infection is estimated to be up to 70 %.

[0004] The virus is transmitted by inhalation, ingestion, coitus, bite wounds or needles. It replicates in mucosal, pulmonary or regional macrophages.

[0005] Subclinically, the disease results in resolution or persistent infection. Persistently infected animals shed virus in oral/pharyngeal fluids, blood, feces, urine and semen.

[0006] Clinical symptoms in sows relate to abortion or premature farrowing with weak live-born pigs, stillborn pigs and autolyzed fetuses. Infected neonatal pigs have a high mortality or suffer from pneumonia. The subsequent nursery and growth of pigs is complicated by pneumonia, concurrent bacterial infections and increased mortality. Boars are prone to fever and morphological changes in semen.

[0007] Like for all arteriviruses, the PRRS virus genome is a single positive-stranded RNA molecule of about 15 kilobases. ORFs (open reading frame) 1 a and 1 b encode replicases, ORFs 2 to 5 putative glycoproteins (gp 1 to 4), ORF 6 a membrane protein (M) and ORF 7 codes for a nucleocapsid protein (N).

[0008] The original descriptions of PRRS infection in the USA (isolated viral agent designated Accession No. ATCC VR-2332, deposited Jul. 18, 1991 at the American Type Culture Collection in Rockville, Md., USA, Genbank U 87392 U00153) and Europe (WO 92/21375, isolate Lelystad Agent (CDI-NL-2.91), deposited Jun. 5, 1991 with the Institute Pasteur, Paris, Accession No. I-1102) identified viruses that had genomic and serological differences. Comparison demonstrated that both had a common ancestor which had diverged before the clinical disease was described in the late 1980's. Full-length genomic sequences have been reported for a number of PRRS viruses and complete structural protein-coding regions thereof (Snijder E. J. and J. J. M. Meulenberg, 1998, J. Gen. Virol. 79(5):961-971; Meulenberg, J. J. M. et al., 1993, Virology 192:62-72; Conzelmann K. K. et al., 1993, Virology 103:329-339; Murtaugh, M. P. et al., 1995, Arch. Virol. 140:1451-1460; Kapur V. et al., 1996, J. Gen. Virol. 77:1271-1276). PRRS virus can be replicated in vitro in pig lung macrophages, monocytes, glial cells and two MA- 104 cell subpopulations (embryonic monkey kidney cell) known as CL-2621 and MARC-145 (Rossow, K. D., 1998, Vet. Pathol 35:1-20). Recombinant means for generating infectious PRRS clones are also available (EP 0 839 912 A1).

[0009] For protecting pigs, live attenuated (e.g., Ingelvac® PRRS MLV, Boehringer Ingelheim) PRRS vaccines are commercially available. The Ingelvac® PRRS MLV vaccine comprises passage 70 of ATCC VR-2332 which was deposited with the American Tissue Culture Collection under Accession No. ATCC VR-2495.

[0010] Killed vaccines (inactivated whole virus) or subunit vaccines (conventionally purified or heterologously expressed purified viral proteins) are most often inferior to live vaccines in their efficacy to produce a full protective immune response even in the presence of adjuvants. For PRRS it has been demonstrated, that in comparison to the currently available killed vaccines, the attenuated vaccines induce an immunity against the disease which lasts longer and is more efficient (Snijder et al., referenced above). The present live PRRS vaccines are attenuated conventionally by serially passaging the virus in appropriate host cells until pathogenicity is lost (EP 0529584 B1). Present live PRRS vaccines still leave ample room for improvement. For one, they do not prevent reinfection. Secondly, they do not allow serological discrimination between vaccinated animals and animals infected with the field virus. But most important of all, live vaccines from complete microorganisms, although attenuated, can be associated with serious safety problems. This holds especially true for RNA viruses such as the PRRS virus, which are considered to have high rates of mutation due to imprecise replication of the RNA genome resulting from a lack of proofreading by the RNA replication enzyme.

[0011] A potential reversion of attenuated live viruses can pose a serious threat to vaccinated animals. For conventionally derived attenuated viruses wherein the attenuation is attained by conventional multiple passaging, the molecular origin as well as the genetic stability remains unknown and the outbreak of revertants is unpredictable.

[0012] Therefore, the technical problem underlying this invention was to provide PRRS viruses less likely to revert to wild type viruses.

SUMMARY OF THE INVENTION

[0013] The present invention relates to live PRRS viruses which are attenuated by amino acid mutations on specific sites of the viral protein encoded by the open reading frame (ORF) selected from the group of ORF 1 a, ORF 1 b and/or ORF 2. The invention also pertains to nucleotide sequences encoding said viruses, methods of generating such viruses and their use for the preparation of a pharmaceutical composition for the prophylaxis and treatment of PRRS infections.

BRIEF DESCRIPTION OF THE FIGURES

[0014]FIG. 1: Amino acid sequence of ORF 1 a of ATCC VR-2332 (SEQ ID NO:1) with preferred attenuation sites according to the invention marked.

[0015]FIG. 2: Amino acid sequence of ORF 1 b of ATCC VR-2332 (SEQ ID NO:2) with preferred attenuation sites according to the invention marked.

[0016]FIG. 3: Amino acid sequence of ORF 2 of ATCC VR-2332 (SEQ ID NO:3) with preferred attenuation sites according to the invention marked.

[0017]FIG. 4: Nucleotide sequence of ORF 1 a of ATCC VR-2332 (SEQ ID NO:4) with preferred attenuation sites according to the invention in bold and most preferred sites underlined.

[0018]FIG. 5: Nucleotide sequence of ORF 1 b of ATCC VR-2332 (SEQ ID NO:5) with preferred attenuation sites according to the invention in bold and most preferred sites underlined.

[0019]FIG. 6: Nucleotide sequence of ORF 2 of ATCC VR-2332 (SEQ ID NO:6) with preferred attenuation sites according to the invention in bold and most preferred sites underlined.

DETAILED DESCRIPTION OF THE INVENTION

[0020] The solution to the above technical problem is achieved by the description and the embodiments characterized in the claims.

[0021] Before the embodiments of the present invention it must be noted that as used herein and in the appended claims, the singular forms “a”, “an”, and “the” include plural reference unless the context clearly dictates otherwise. Thus, for example, reference to “a PRRS virus” includes a plurality of such PRRS viruses, reference to the “cell” is a reference to one or more cells and equivalents thereof known to those skilled in the art, and so forth. Unless defined otherwise, all technical and scientific terms used herein have the same meanings as commonly understood by one of ordinary skill in the art to which this invention belongs.

[0022] Although any methods and materials similar or equivalent to those described herein can be used in the practice or testing of the present invention, the preferred methods, devices, and materials are now described. All publications mentioned herein are incorporated herein by reference for the purpose of describing and disclosing the cell lines, vectors, and methodologies which are reported in the publications which might be used in connection with the invention. Nothing herein is to be construed as an admission that the invention is not entitled to antedate such disclosure by virtue of prior invention.

[0023] It has surprisingly been found that PRRS viruses comprise specific genomic sites in some open reading frames that consistently revert to the amino acids encoded by ATCC VR-2332 at that position. The evolutionary pressure on this from now on called “virulence specific site” or simply referred to as “site of the invention or just “site” is immense. For two revertant strains of ATCC VR-2495, it was possible to demonstrate for the first time that the amino acid mutation to the amino acid of ATCC VR-2332 at this virulence specific site occurred geographically independently in both, the USA and Europe.

[0024] Live vaccines with defined mutations as a basis for attenuation according to the invention avoid the disadvantages of the present generation of attenuated vaccines. A further advantage of said attenuating mutations lies in their known molecular uniqueness which allows for use as distinctive labels for attenuated pestiviruses and to distinguish them from pestiviruses from the field.

[0025] The amino acid and nucleotide sequence of the conventionally attenuated virus ATCC VR-2495 were compared to ATCC VR-2332. To identify the virulence specific sites, the two mentioned virulent revertants were compared to each other and ATCC VR-2332 as well as ATCC VR-2495.

[0026] This allowed for the identification of the virulence specific site on an individual viral protein that is implicated in the virulence of PRRS viruses.

[0027] In consequence, one aspect of the invention relates to live PRRS viruses which are not ATCC VR-2495 and which are less virulent than the PRRS virus ATCC VR-2332 that are characterized in that they comprise a protein encoded by the open reading frame (ORF) selected from the group of ORF 1 a as described in FIG. 1 for said ATCC VR-2332 strain, ORF 1 b as described in FIG. 2 for said ATCC VR-2332 strain, and/or ORF 2 as described in FIG. 3 for said ATCC VR-2332 strain, wherein at least one of the amino acids at the identified virulence specific sites is not identical to at least one of the amino acids of the strain ATCC VR-2332 at said corresponding positions.

[0028] The numbering of amino acids and nucleotides (nt) is according to the database entry of VR-2332. FIGS. 1, 2 and 3 provide information that is representative for all PRRS strains and allows visualization of the invention and identification of the preferred amino acids and preferred site in all PRRS viruses that might be numbered differently. Identification of these positions is achieved by identifying preserved characteristic identical amino acids in a PRRS strain of interest and the listed reference strain and subsequently determining the position of the site of the virus of interest relative to the site in FIG. 1, 2 or 3.

[0029] Three of said sites have been identified for the protein encoded by the viral ORF 1 a, ORF 1 b and ORF 2 which are depicted for ATCC VR-2332 in FIGS. 1, 2 and 3, respectively.

[0030] Another aspect of the invention relates to a live attenuated PRRS virus comprising ORF 1 a, ORF 1 b and ORF 2 essentially as in ATCC VR-2332 which is not ATCC VR-2495, characterized in that at least one of the amino acids in position 321 to 341 of the protein encoded by ORF 1 a is not identical to the amino acid(s) of the strain ATCC VR-2332 at said corresponding position(s) as described in FIG. 1 and/or at least one of the amino acids in position 936 to 956 of the protein encoded by ORF 1 b is not identical to the amino acid(s) of the strain ATCC VR-2332 at said corresponding position(s) as described in FIG. 2 and/or at least one of the amino acids in position 1 to 20 of the protein encoded by ORF 2 is not identical to the amino acid(s) of the strain ATCC VR-2332 at said corresponding position(s) as described in FIG. 3. Thus, at the amino acid site 321-341 encoded by ORF 1 a (nt 961-1023), amino acid site 936-956 encoded by ORF 1 b (nt 2806-2868), or amino acid site 1-20 encoded ORF 2 (nt 1-60) (See FIG. 4, 5 or 6, respectively), the coding nucleotide triplet for one amino acid, or for more than one amino acids is/are mutated resulting in one or several changes in the sequence at said site either on the nucleic acid level or in addition and preferentially also on the amino acid level, whereby up to all nucleotide or amino acid positions at a said site may be mutated. Viruses where either one, two, or all three of said sites are mutated are embraced by the present invention.

[0031] “Mutation” means the replacement of an amino acid for another or the replacement of the coding nucleotide by another (e.g. C for a T), i.e., a so-called “substitution”, preferably in a way that the encoded amino acid is changed, or any other mutation such as “deletion” or “insertion”. The mutation is always carried out in the coding nucleotide sequence.

[0032] Said mutations may be carried out by standard methods known in the art, e.g. site directed mutagenesis (see e.g. Sambrook et al.(1989) Molecular Cloning: A Laboratory Manual, 2^(nd) ed., Cold Spring Harbor Laboratory Press, Cold Spring Harbor, N.Y.) of an infectious copy as described (e.g. Meulenberg et al., Adv. Exp. Med. Biol, 1998, 440:199-206).

[0033] “Essentially” means at least 75% of the sequence, preferably 85%, most preferably all of the sequence except the “sites” according to the invention is identical to ATCC VR-2332. However, additional nucleic acids coding for amino acids outside said sites according to the invention may also be mutated. Said virus according to the invention is still fulfilling the criteria according to the invention, i.e., being less likely to revert to wild type and also less virulent than ATCC VR-2332.

[0034] A live PRRS virus according to the invention refers to a PRRS virus as defined in Snijder et al. (referenced above) that is capable of infecting swine and capable of replication in swine.

[0035] The conventionally attenuated ATCC VR-2495 virus is specifically disclaimed. It is not a virus according to the invention and is specifically excluded from the scope of the claims. The vaccine comprising ATCC VR-2495 virus is commercially available from the Boehringer Ingelheim Vetmedica company (Ingelvac® PRRS MLV). Most of its sequence is publicly available (Genbank AJ 223082).

[0036] The site and amino acids of particular importance to the invention are by no means limited to the exact position as defined for the ATCC VR-2332 strain but are simply used in an exemplary manner to point out the preferred amino acids being at that position or corresponding to that position in other PRRS strains. For different PRRS viruses the numbering of the positions of the preferred amino acids might be different but an expert in the field of the molecular biology of viruses of the family arteriviridae will easily identify these preferred amino acids by their position relative to the other conserved amino acids of said proteins.

[0037] The term “less virulent than the PRRS virus ATCC VR-2332” is to be understood in terms of a comparison of clinical symptoms of the virus of interest with ATCC VR-2332. A preferred procedure for determining if a PRRS virus is less virulent than the PRRS virus ATCC VR-2332 is listed in Example 1. Not all possible preferred amino acid mutations at the virulence specific site might be implicated in reducing virulence. The procedure of Example 1 provides a precise and straight forward experimental setup for determining whether a live PRRS virus, that comprises the protein according to the teaching of the invention, is less virulent than ATCC VR-2332.

[0038] The virulence specific site was identified by the reversion of at least one amino acid from the attenuated virus to the amino acid of ATCC VR-2332. This particular amino acid is part of a larger secondary peptide structure such as an alpha helix or a β sheet or a hairpin β motif or others. It is therefore highly probable that neighboring amino acids are also involved in the regulation of virulence of that protein. An expert in the field of protein chemistry would therefore expect a high probability of identifying further amino acids with virulence-implicated properties within the vicinity of 10 amino acids to the left and right of the originally identified amino acid position. Ten to 20 amino acids is the typical range for peptide motifs in proteins. Therefore, preferred viruses according to the invention comprise nucleotides encoding the protein described in FIG. 1 in an exemplary manner or corresponding thereto in other strains, wherein the virulence specific site comprises 10 amino acids upstream and 10 amino acids downstream of the originally identified amino acid position. More preferred are those viruses as mentioned above, wherein the virulence specific site comprises 5 amino acids upstream and 5 amino acids downstream of the originally identified amino acid position. Most preferred are those viruses as mentioned above, wherein the virulence specific site comprises 3 amino acids upstream and 3 amino acids downstream of the originally identified amino acid position.

[0039] With the teaching of the present invention, it is possible to generate attenuated PRRS strains from virulent strains by mutating the nucleotides encoding amino acids at the virulence specific site. Still, the safety problem associated with the high frequency of mutation in RNA viruses remains. This problem can be greatly reduced by deleting specific amino acids in the virulence specific site of the virus protein. The invention, therefore, relates to PRRS viruses as mentioned above that are characterized in that at least one of the amino acids in the virulence specific site of the viral protein is deleted. The term “deleted” is to be understood as being absent in comparison to the amino acids referenced in the figure at that or those position(s). Thus, according to the invention, “deletion” means the removal of one or several nucleotides or amino acids.

[0040] In a more preferred embodiment the invention therefore relates to a live attenuated PRRS virus according to the invention, characterized in that at least one of the amino acids in position 321 to 341 of the protein encoded by ORF 1 a is deleted and/or at least one of the amino acids in position 936 to 956 of the protein encoded by ORF 1 b is deleted and/or at least one of the amino acids in position 1 to 20 the protein encoded by ORF 2 is deleted. Thus, either at the amino acid site 321-341 encoded by ORF 1 a , amino acid site 936-956 encoded by ORF 1 b , or amino acid site 1-20 encoded by ORF 2 or at all three sites the coding nucleotide triplet for one amino acid, or for more than one amino acids is/are mutated resulting in one or several changes in the sequence at said site either on the nucleic acid level or in addition and preferentially also on the amino acid level, whereby up to all nucleotide or amino acid positions at a said site may be mutated. Viruses where either one, two, or all three of said sites are mutated are embraced by the present invention.

[0041] For the identified virulence specific site on the particular PRRS virus protein it has been demonstrated in a preferred example that at least one amino acid is under high mutational pressure and involved in the virulent properties of revertants of ATCC VR-2332. This individual amino acid position is a most preferred embodiment of the invention.

[0042] Therefore, in a most preferred embodiment, the present invention relates to a live attenuated PRRS virus according to the invention which is not ATCC VR-2495 and which is less virulent than ATCC VR-2332, characterized in that the amino acid in position 331 of the protein encoded by ORF 1 a and/or the amino acid in position 946 of the protein encoded by ORF 1 b and/or the amino acid in position 10 of the protein encoded by ORF 2 is/are not identical to the amino acid of the strain ATCC VR-2332 at said corresponding position. Thus, either at the site 331 of ORF 1 a , site 946 of ORF 1 b , or site 10 of ORF 2 or at all three sites the coding nucleotide triplet for one amino acid or the amino acid is mutated resulting in one to three mutations at said site(s) (See FIG. 4, 5 or 6, respectively).

[0043] For the reasons presented above, it is safer and preferable to avoid the reversion of altered amino acids to the virulent type by simply deleting the amino acid that is prone to revert.

[0044] Therefore, the present invention relates in this most preferred embodiment to a live attenuated PRRS virus according to the invention, characterized in that the amino acid in position 331 of the protein encoded by ORF 1 a and/or the amino acid in position 946 of the protein encoded by ORF 1 b and/or the amino acid in position 10 of the protein encoded by ORF 2 is/are deleted, in other words, absent when compared to that position in ATCC VR-2332.

[0045] A further, most preferred embodiment is a live attenuated PRRS virus according to the invention, characterized in that the amino acid in position 331 of the protein encoded by ORF 1 a , i.e., the coding triplet is deleted. A further, most preferred embodiment is a live attenuated PRRS virus according to the invention, characterized in that the amino acid in position 946 of the protein encoded by ORF 1 b , i.e., the coding triplet is deleted. A further, most preferred embodiment is a live attenuated PRRS virus according to the invention, characterized in that the amino acid in position 10 of the protein encoded by ORF 2, i.e., the coding triplet is deleted (See FIG. 4, 5 or 6, respectively). Said most preferred virus is identical to ATCC VR-2332 in all other positions.

[0046] The teaching of the present invention now enables the expert to recombinantly produce infectious clones of PRRS viruses (PRRSV) that are less virulent than ATCC VR-2332 and are useful for preparing a live pharmaceutical composition. All information required to produce recombinant infectious clones of positive strand RNA viruses is readily available in the art, particularly for the PRRSV. For example, the European patent application EP 0 839 912 of Meulenberg et al., which is referenced herewith in its entirety, provides a clear teaching for the preparation of recombinant live PRRS viruses. Therefore, in a further aspect, the present invention relates to nucleotide sequences coding for a virus according to the invention. Due to the degeneration of the genetic code multiple nucleotide variants may result in the identical amino acid translation. Those degenerate variants are also encompassed by the invention.

[0047] As mentioned in the introductory pages, it is important for the health management of pigs to be able to distinguish between the less virulent live vaccine strain of the pharmaceutical composition and the virulent wild type virus infections. This is often difficult, especially when clinical symptoms of a field infection are not that specific or superimposed by other infections or the time period for observation and evaluation is short. The recombinant generation of the viruses of interest allows for the introduction of modifications in the genetic code that establishes a serological marker and/or a virulence marker. A serological marker refers to an antigenically detectable molecule such as a peptide, a protein, glycoprotein that can be isolated from infected cells or body fluids such as but not limited to pharyngeal or nasal fluids or urine. A virulence marker is to be understood as a marker in the genetic code that can be identified by recombinant analytical methods such as but not limited to PCR and conventional sequencing. Therefore, in a preferred embodiment, the present invention relates to a nucleotide sequence according to the invention, wherein the nucleotide sequence has been modified to encode a virulence marker and/or a serological marker. Particularly, the mutations or deletions introduced for the purpose of attenuating virulence are useful as virulence and serological markers. By monitoring these mutations in the disclosed virulence specific sites it is possible to predict the emergence of possibly virulent revertants at an early stage.

[0048] It is more preferred that the nucleotide sequences of the invention are such that the nucleotide sequence encoding said marker is located within any of the open reading frames encoding structural viral proteins.

[0049] A further aspect of the present invention relates to a method for the generation of an infectious live attenuated PRRS virus according to the invention, said method comprising producing a recombinant nucleic acid as described above comprising at least one full-length DNA copy or in vitro-transcribed RNA copy or a derivative of either.

[0050] Another preferred embodiment according to the invention relates to a method according to the invention, wherein specific mutations are inserted with molecular biology methods, characterized in that the nucleic acid corresponding to amino acid positions 321 to 341 of ORF 1 a and/or the nucleic acid corresponding to amino acid positions 936 to 956 of ORF and/or the nucleic acid corresponding to amino acid positions 1 to 20 of ORF 2 is mutated in such a way that at least one nucleotide at said positions is substituted or deleted.

[0051] Another important aspect of the invention is a pharmaceutical composition comprising a PRRS virus according to the invention and a pharmaceutically acceptable carrier.

[0052] A “pharmaceutical composition” essentially consists of one or more ingredients capable of modifying physiological e.g. immunological functions of the organism it is administered to or of organisms living in or on its surface including but not restricted to antibiotics or antiparasitics, as well as other constituents added to it in order to achieve certain other objectives including, but not limited to, processing traits, sterility, stability, feasibility to administer the composition via enteral or parenteral routes such as oral, intranasal, intravenous, intramuscular, subcutaneous, intradermal or other suitable route, tolerance after administration, controlled release properties.

[0053] A pharmaceutically acceptable carrier can contain physiologically acceptable compounds that act, for example, to stabilize or to increase the absorption or form part of a slow release formulation of the PRRS virus according to the invention. Such physiologically acceptable compounds include, for example, carbohydrates, such as glucose, sucrose or dextrans, antioxidants, such as ascorbic acid or glutathione, chelating agents, low molecular weight proteins or other stabilizers or excipients (see also e.g. Remington's Pharmaceutical Sciences (1990). 18th ed. Mack Publ., Easton). One skilled in the art would know that the choice of a pharmaceutically acceptable carrier, including a physiologically acceptable compound, depends, for example, on the route of administration of the composition.

[0054] A further aspect of the invention relates to the use of the viruses according to the invention. With the availability of the live attenuated PRRS viruses of the invention it is now possible to use these in the manufacture of a vaccine for the prophylaxis and treatment of PRRS infections. Their defined molecular basis of attenuation makes them superior to the present conventionally attenuated viruses. Especially the use of viruses according to the invention that comprise deletions in the virulence specific sites is preferred since deletions are less prone to revert.

[0055] The following example serves to further illustrate the present invention; but the same should not be construed as limiting the scope of the invention disclosed herein.

EXAMPLE 1

[0056] Establishment of Attenuation

[0057] This example provides a clear guidance for the comparison of the virulent character of two different strains of PRRS viruses.

[0058] At least 10 gilts per group are included in each trial, which are derived from a PRRS free farm.

[0059] Animals are tested free of PRRS virus specific serum antibodies and negative for PRRSV. All animals included in the trial are of the same source and breed. The allocation of the animals to the groups is randomized.

[0060] Challenge is performed at day 90 of pregnancy with intranasal application of 1 ml PRRSV with 10⁵ TDCID₅₀ (third passage) per nostril. There are at least three groups for each test setup:

[0061] One group for ATCC VR-2332 challenge; one test group for challenge with the possibly attenuated virus; and one strict control group.

[0062] The study is deemed valid when the strict controls stay PRRS negative over the time course of the study and at least 25% less life healthy piglets are born in the ATCC VR-2332 challenged group compared to the strict controls.

[0063] Attenuation, in other words less virulence, is defined as the statistical significant change of one or more parameters determining reproductive performance:

[0064] Significant reduction in at least one of the following parameters for the test group (possibly attenuated virus) compared to the ATCC VR-2332 infected group is preferred:

[0065] frequency of stillborns

[0066] abortion at or before day 112 of pregnancy

[0067] number of mummified piglets

[0068] number of less live and weak piglets

[0069] preweaning mortality or furthermore a significant increase in one of the following parameters for the test group compared to the ATCC VR-2332 infected group is preferred:

[0070] number of piglets weaned per sow

[0071] number of live healthy piglets born per sow.

1 6 1 2502 PRT Porcine reproductive and respiratory syndrome virus 1 Met Ser Gly Ile Leu Asp Arg Cys Thr Cys Thr Pro Asn Ala Arg Val 1 5 10 15 Phe Met Ala Glu Gly Gln Val Tyr Cys Thr Arg Cys Leu Ser Ala Arg 20 25 30 Ser Leu Leu Pro Leu Asn Leu Gln Val Ser Glu Leu Gly Val Leu Gly 35 40 45 Leu Phe Tyr Arg Pro Glu Glu Pro Leu Arg Trp Thr Leu Pro Arg Ala 50 55 60 Phe Pro Thr Val Glu Cys Ser Pro Ala Gly Ala Cys Trp Leu Ser Ala 65 70 75 80 Ile Phe Pro Ile Ala Arg Met Thr Ser Gly Asn Leu Asn Phe Gln Gln 85 90 95 Arg Met Val Arg Val Ala Ala Glu Leu Tyr Arg Ala Gly Gln Leu Thr 100 105 110 Pro Ala Val Leu Lys Ala Leu Gln Val Tyr Glu Arg Gly Cys Arg Trp 115 120 125 Tyr Pro Ile Val Gly Pro Val Pro Gly Val Ala Val Phe Ala Asn Ser 130 135 140 Leu His Val Ser Asp Lys Pro Phe Pro Gly Ala Thr His Val Leu Thr 145 150 155 160 Asn Leu Pro Leu Pro Gln Arg Pro Lys Pro Glu Asp Phe Cys Pro Phe 165 170 175 Glu Cys Ala Met Ala Thr Val Tyr Asp Ile Gly His Asp Ala Val Met 180 185 190 Tyr Val Ala Glu Arg Lys Val Ser Trp Ala Pro Arg Gly Gly Asp Glu 195 200 205 Val Lys Phe Glu Ala Val Pro Gly Glu Leu Lys Leu Ile Ala Asn Arg 210 215 220 Leu Arg Thr Ser Phe Pro Pro His His Thr Val Asp Met Ser Lys Phe 225 230 235 240 Ala Phe Thr Ala Pro Gly Cys Gly Val Ser Met Arg Val Glu Arg Gln 245 250 255 His Gly Cys Leu Pro Ala Asp Thr Val Pro Glu Gly Asn Cys Trp Trp 260 265 270 Ser Leu Phe Asp Leu Leu Pro Leu Glu Val Gln Asn Lys Glu Ile Arg 275 280 285 His Ala Asn Gln Phe Gly Tyr Gln Thr Lys His Gly Val Ser Gly Lys 290 295 300 Tyr Leu Gln Arg Arg Leu Gln Val Asn Gly Leu Arg Ala Val Thr Asp 305 310 315 320 Leu Asn Gly Pro Ile Val Val Gln Tyr Phe Ser Val Lys Glu Ser Trp 325 330 335 Ile Arg His Leu Lys Leu Ala Gly Glu Pro Ser Tyr Ser Gly Phe Glu 340 345 350 Asp Leu Leu Arg Ile Arg Val Glu Pro Asn Thr Ser Pro Leu Ala Asp 355 360 365 Lys Glu Glu Lys Ile Phe Arg Phe Gly Ser His Lys Trp Tyr Gly Ala 370 375 380 Gly Lys Arg Ala Arg Lys Ala Arg Ser Cys Ala Thr Ala Thr Val Ala 385 390 395 400 Gly Arg Ala Leu Ser Val Arg Glu Thr Arg Gln Ala Lys Glu His Glu 405 410 415 Val Ala Gly Ala Asn Lys Ala Glu His Leu Lys His Tyr Ser Pro Pro 420 425 430 Ala Glu Gly Asn Cys Gly Trp His Cys Ile Ser Ala Ile Ala Asn Arg 435 440 445 Met Val Asn Ser Lys Phe Glu Thr Thr Leu Pro Glu Arg Val Arg Pro 450 455 460 Pro Asp Asp Trp Ala Thr Asp Glu Asp Leu Val Asn Ala Ile Gln Ile 465 470 475 480 Leu Arg Leu Pro Ala Ala Leu Asp Arg Asn Gly Ala Cys Thr Ser Ala 485 490 495 Lys Tyr Val Leu Lys Leu Glu Gly Glu His Trp Thr Val Thr Val Thr 500 505 510 Pro Gly Met Ser Pro Ser Leu Leu Pro Leu Glu Cys Val Gln Gly Cys 515 520 525 Cys Gly His Lys Gly Gly Leu Gly Ser Pro Asp Ala Val Glu Val Ser 530 535 540 Gly Phe Asp Pro Ala Cys Leu Asp Arg Leu Ala Glu Val Met His Leu 545 550 555 560 Pro Ser Ser Ala Ile Pro Ala Ala Leu Ala Glu Met Ser Gly Asp Ser 565 570 575 Asp Arg Ser Ala Ser Pro Val Thr Thr Val Trp Thr Val Ser Gln Phe 580 585 590 Phe Ala Arg His Ser Gly Gly Asn His Pro Asp Gln Val Arg Leu Gly 595 600 605 Lys Ile Ile Ser Leu Cys Gln Val Ile Glu Asp Cys Cys Cys Ser Gln 610 615 620 Asn Lys Thr Asn Arg Val Thr Pro Glu Glu Val Ala Ala Lys Ile Asp 625 630 635 640 Leu Tyr Leu Arg Gly Ala Thr Asn Leu Glu Glu Cys Leu Ala Arg Leu 645 650 655 Glu Lys Ala Arg Pro Pro Arg Val Ile Asp Thr Ser Phe Asp Trp Asp 660 665 670 Val Val Leu Pro Gly Val Glu Ala Ala Thr Gln Thr Ile Lys Leu Pro 675 680 685 Gln Val Asn Gln Cys Arg Ala Leu Val Pro Val Val Thr Gln Lys Ser 690 695 700 Leu Asp Asn Asn Ser Val Pro Leu Thr Ala Phe Ser Leu Ala Asn Tyr 705 710 715 720 Tyr Tyr Arg Ala Gln Gly Asp Glu Val Arg His Arg Glu Arg Leu Thr 725 730 735 Ala Val Leu Ser Lys Leu Glu Lys Val Val Arg Glu Glu Tyr Gly Leu 740 745 750 Met Pro Thr Glu Pro Gly Pro Arg Pro Thr Leu Pro Arg Gly Leu Asp 755 760 765 Glu Leu Lys Asp Gln Met Glu Glu Asp Leu Leu Lys Leu Ala Asn Ala 770 775 780 Gln Thr Thr Ser Asp Met Met Ala Trp Ala Val Glu Gln Val Asp Leu 785 790 795 800 Lys Thr Trp Val Lys Asn Tyr Pro Arg Trp Thr Pro Pro Pro Pro Pro 805 810 815 Pro Lys Val Gln Pro Arg Lys Thr Lys Pro Val Lys Ser Leu Pro Glu 820 825 830 Arg Lys Pro Val Pro Ala Pro Arg Arg Lys Val Gly Ser Asp Cys Gly 835 840 845 Ser Pro Val Ser Leu Gly Gly Asp Val Pro Asn Ser Trp Glu Asp Leu 850 855 860 Ala Val Ser Ser Pro Phe Asp Leu Pro Thr Pro Pro Glu Pro Ala Thr 865 870 875 880 Pro Ser Ser Glu Leu Val Ile Val Ser Ser Pro Gln Cys Ile Phe Arg 885 890 895 Pro Ala Thr Pro Leu Ser Glu Pro Ala Pro Ile Pro Ala Pro Arg Gly 900 905 910 Thr Val Ser Arg Pro Val Thr Pro Leu Ser Glu Pro Ile Pro Val Pro 915 920 925 Ala Pro Arg Arg Lys Phe Gln Gln Val Lys Arg Leu Ser Ser Ala Ala 930 935 940 Ala Ile Pro Pro Tyr Gln Asp Glu Pro Leu Asp Leu Ser Ala Ser Ser 945 950 955 960 Gln Thr Glu Tyr Glu Ala Ser Pro Pro Ala Pro Pro Gln Ser Gly Gly 965 970 975 Val Leu Gly Val Glu Gly His Glu Ala Glu Glu Thr Leu Ser Glu Ile 980 985 990 Ser Asp Met Ser Gly Asn Ile Lys Pro Ala Ser Val Ser Ser Ser Ser 995 1000 1005 Ser Leu Ser Ser Val Arg Ile Thr Arg Pro Lys Tyr Ser Ala Gln Ala 1010 1015 1020 Ile Ile Asp Ser Gly Gly Pro Cys Ser Gly His Leu Gln Glu Val Lys 1025 1030 1035 1040 Glu Thr Cys Leu Ser Val Met Arg Glu Ala Cys Asp Ala Thr Lys Leu 1045 1050 1055 Asp Asp Pro Ala Thr Gln Glu Trp Leu Ser Arg Met Trp Asp Arg Val 1060 1065 1070 Asp Met Leu Thr Trp Arg Asn Thr Ser Val Tyr Gln Ala Ile Cys Thr 1075 1080 1085 Leu Asp Gly Arg Leu Lys Phe Leu Pro Lys Met Ile Leu Glu Thr Pro 1090 1095 1100 Pro Pro Tyr Pro Cys Glu Phe Val Met Met Pro His Thr Pro Ala Pro 1105 1110 1115 1120 Ser Val Gly Ala Glu Ser Asp Leu Thr Ile Gly Ser Val Ala Thr Glu 1125 1130 1135 Asp Val Pro Arg Ile Leu Glu Lys Ile Glu Asn Val Gly Glu Met Ala 1140 1145 1150 Asn Gln Gly Pro Leu Ala Phe Ser Glu Asp Lys Pro Val Asp Asp Gln 1155 1160 1165 Leu Val Asn Asp Pro Arg Ile Ser Ser Arg Arg Pro Asp Glu Ser Thr 1170 1175 1180 Ser Ala Pro Ser Ala Gly Thr Gly Gly Ala Gly Ser Phe Thr Asp Leu 1185 1190 1195 1200 Pro Pro Ser Asp Gly Ala Asp Ala Asp Gly Gly Gly Pro Phe Arg Thr 1205 1210 1215 Val Lys Arg Lys Ala Glu Arg Leu Phe Asp Gln Leu Ser Arg Gln Val 1220 1225 1230 Phe Asp Leu Val Ser His Leu Pro Val Phe Phe Ser Arg Leu Phe Tyr 1235 1240 1245 Pro Gly Gly Gly Tyr Ser Pro Gly Asp Trp Gly Phe Ala Ala Phe Thr 1250 1255 1260 Leu Leu Cys Leu Phe Leu Cys Tyr Ser Tyr Pro Ala Phe Gly Ile Ala 1265 1270 1275 1280 Pro Leu Leu Gly Val Phe Ser Gly Ser Ser Arg Arg Val Arg Met Gly 1285 1290 1295 Val Phe Gly Cys Trp Leu Ala Phe Ala Val Gly Leu Phe Lys Pro Val 1300 1305 1310 Ser Asp Pro Val Gly Ala Ala Cys Glu Phe Asp Ser Pro Glu Cys Arg 1315 1320 1325 Asn Ile Leu His Ser Phe Glu Leu Leu Lys Pro Trp Asp Pro Val Arg 1330 1335 1340 Ser Leu Val Val Gly Pro Val Gly Leu Gly Leu Ala Ile Leu Gly Arg 1345 1350 1355 1360 Leu Leu Gly Gly Ala Arg Cys Ile Trp His Phe Leu Leu Arg Leu Gly 1365 1370 1375 Ile Val Ala Asp Cys Ile Leu Ala Gly Ala Tyr Val Leu Ser Gln Gly 1380 1385 1390 Arg Cys Lys Lys Cys Trp Gly Ser Cys Ile Arg Thr Ala Pro Asn Glu 1395 1400 1405 Val Ala Phe Asn Val Phe Pro Phe Thr Arg Ala Thr Arg Ser Ser Leu 1410 1415 1420 Ile Asp Leu Cys Asp Arg Phe Cys Ala Pro Lys Gly Met Asp Pro Ile 1425 1430 1435 1440 Phe Leu Ala Thr Gly Trp Arg Gly Cys Trp Ala Gly Arg Ser Pro Ile 1445 1450 1455 Glu Gln Pro Ser Glu Lys Pro Ile Ala Phe Ala Gln Leu Asp Glu Lys 1460 1465 1470 Lys Ile Thr Ala Arg Thr Val Val Ala Gln Pro Tyr Asp Pro Asn Gln 1475 1480 1485 Ala Val Lys Cys Leu Arg Val Leu Gln Ser Gly Gly Arg Trp Trp Leu 1490 1495 1500 Ser Gly Pro Lys Ser Gly Gln Gly Phe Arg Cys Ser Ile Pro Ser Pro 1505 1510 1515 1520 Phe Phe Pro Thr Gly Val Lys Val Asp Pro Asp Cys Arg Val Val Val 1525 1530 1535 Asp Pro Asp Thr Phe Thr Ala Ala Leu Arg Ser Gly Tyr Ser Thr Thr 1540 1545 1550 Asn Leu Val Leu Gly Val Gly Asp Phe Ala Gln Leu Asn Gly Leu Lys 1555 1560 1565 Ile Arg Gln Ile Ser Lys Pro Ser Gly Gly Gly Pro His Leu Met Ala 1570 1575 1580 Ala Leu His Val Ala Cys Ser Met Ala Leu His Met Leu Ala Gly Ile 1585 1590 1595 1600 Tyr Val Thr Ala Val Gly Ser Cys Gly Thr Gly Thr Asn Asp Pro Trp 1605 1610 1615 Cys Ala Asn Pro Phe Ala Val Pro Gly Tyr Gly Pro Gly Ser Leu Cys 1620 1625 1630 Thr Ser Arg Leu Cys Ile Ser Gln His Gly Leu Thr Leu Pro Leu Thr 1635 1640 1645 Ala Leu Val Ala Gly Phe Gly Ile Gln Glu Ile Ala Leu Val Val Leu 1650 1655 1660 Ile Phe Val Ser Ile Gly Gly Met Ala His Arg Leu Ser Cys Lys Ala 1665 1670 1675 1680 Asp Met Leu Cys Val Leu Leu Ala Ile Ala Ser Tyr Val Trp Val Pro 1685 1690 1695 Leu Thr Trp Leu Leu Cys Val Phe Pro Cys Trp Leu Arg Cys Phe Ser 1700 1705 1710 Leu His Pro Leu Thr Ile Leu Trp Leu Val Phe Phe Leu Ile Ser Val 1715 1720 1725 Asn Met Pro Ser Gly Ile Leu Ala Met Val Leu Leu Val Ser Leu Trp 1730 1735 1740 Leu Leu Gly Arg Tyr Thr Asn Val Ala Gly Leu Val Thr Pro Tyr Asp 1745 1750 1755 1760 Ile His His Tyr Thr Ser Gly Pro Arg Gly Val Ala Ala Leu Ala Thr 1765 1770 1775 Ala Pro Asp Gly Thr Tyr Leu Ala Ala Val Arg Arg Ala Ala Leu Thr 1780 1785 1790 Gly Arg Thr Met Leu Phe Thr Pro Ser Gln Leu Gly Ser Leu Leu Glu 1795 1800 1805 Gly Ala Phe Arg Thr Arg Lys Pro Ser Leu Asn Thr Val Asn Val Ile 1810 1815 1820 Gly Ser Ser Met Gly Ser Gly Gly Val Phe Thr Ile Asp Gly Lys Val 1825 1830 1835 1840 Lys Cys Val Thr Ala Ala His Val Leu Thr Gly Asn Ser Ala Arg Val 1845 1850 1855 Ser Gly Val Gly Phe Asn Gln Met Leu Asp Phe Asp Val Lys Gly Asp 1860 1865 1870 Phe Ala Ile Ala Asp Cys Pro Asn Trp Gln Gly Ala Ala Pro Lys Thr 1875 1880 1885 Gln Phe Cys Thr Asp Gly Trp Thr Gly Arg Ala Tyr Trp Leu Thr Ser 1890 1895 1900 Ser Gly Val Glu Pro Gly Val Ile Gly Lys Gly Phe Ala Phe Cys Phe 1905 1910 1915 1920 Thr Ala Cys Gly Asp Ser Gly Ser Pro Val Ile Thr Glu Ala Gly Glu 1925 1930 1935 Leu Val Gly Val His Thr Gly Ser Asn Lys Gln Gly Gly Gly Ile Val 1940 1945 1950 Thr Arg Pro Ser Gly Gln Phe Cys Asn Val Ala Pro Ile Lys Leu Ser 1955 1960 1965 Glu Leu Ser Glu Phe Phe Ala Gly Pro Lys Val Pro Leu Gly Asp Val 1970 1975 1980 Lys Val Gly Ser His Ile Ile Lys Asp Ile Ser Glu Val Pro Ser Asp 1985 1990 1995 2000 Leu Cys Ala Leu Leu Ala Ala Lys Pro Glu Leu Glu Gly Gly Leu Ser 2005 2010 2015 Thr Val Gln Leu Leu Cys Val Phe Phe Leu Leu Trp Arg Met Met Gly 2020 2025 2030 His Ala Trp Thr Pro Leu Val Ala Val Ser Phe Phe Ile Leu Asn Glu 2035 2040 2045 Val Leu Pro Ala Val Leu Val Arg Ser Val Phe Ser Phe Gly Met Phe 2050 2055 2060 Val Leu Ser Trp Leu Thr Pro Trp Ser Ala Gln Val Leu Met Ile Arg 2065 2070 2075 2080 Leu Leu Thr Ala Ala Leu Asn Arg Asn Arg Trp Ser Leu Ala Phe Phe 2085 2090 2095 Ser Leu Gly Ala Val Thr Gly Phe Val Ala Asp Leu Ala Ala Thr Gln 2100 2105 2110 Gly His Pro Leu Gln Ala Val Met Asn Leu Ser Thr Tyr Ala Phe Leu 2115 2120 2125 Pro Arg Met Met Val Val Thr Ser Pro Val Pro Val Ile Thr Cys Gly 2130 2135 2140 Val Val His Leu Leu Ala Ile Ile Leu Tyr Leu Phe Lys Tyr Arg Gly 2145 2150 2155 2160 Pro His His Ile Leu Val Gly Asp Gly Val Phe Ser Ala Ala Phe Phe 2165 2170 2175 Leu Arg Tyr Phe Ala Glu Gly Lys Leu Arg Glu Gly Val Ser Gln Ser 2180 2185 2190 Cys Gly Met Asn His Glu Ser Leu Thr Gly Ala Leu Ala Met Arg Leu 2195 2200 2205 Asn Asp Glu Asp Leu Asp Phe Leu Met Lys Trp Thr Asp Phe Lys Cys 2210 2215 2220 Phe Val Ser Ala Ser Asn Met Arg Asn Ala Ala Gly Gln Phe Ile Glu 2225 2230 2235 2240 Ala Ala Tyr Ala Lys Ala Leu Arg Val Glu Leu Ala Gln Leu Val Gln 2245 2250 2255 Val Asp Lys Val Arg Gly Thr Leu Ala Lys Leu Glu Ala Phe Ala Asp 2260 2265 2270 Thr Val Ala Pro Gln Leu Ser Pro Gly Asp Ile Val Val Ala Leu Gly 2275 2280 2285 His Thr Pro Val Gly Ser Ile Phe Asp Leu Lys Val Gly Ser Thr Lys 2290 2295 2300 His Thr Leu Gln Ala Ile Glu Thr Arg Val Leu Ala Gly Ser Lys Met 2305 2310 2315 2320 Thr Val Ala Arg Val Val Asp Pro Thr Pro Thr Pro Pro Pro Ala Pro 2325 2330 2335 Val Pro Ile Pro Leu Pro Pro Lys Val Leu Glu Asn Gly Pro Asn Ala 2340 2345 2350 Trp Gly Asp Glu Asp Arg Leu Asn Lys Lys Lys Arg Arg Arg Met Glu 2355 2360 2365 Ala Leu Gly Ile Tyr Val Met Gly Gly Lys Lys Tyr Gln Lys Phe Trp 2370 2375 2380 Asp Lys Asn Ser Gly Asp Val Phe Tyr Glu Glu Val His Asn Asn Thr 2385 2390 2395 2400 Asp Glu Trp Glu Cys Leu Arg Val Gly Asp Pro Ala Asp Phe Asp Pro 2405 2410 2415 Glu Lys Gly Thr Leu Cys Gly His Val Thr Ile Glu Asn Lys Ala Tyr 2420 2425 2430 His Val Tyr Thr Ser Pro Ser Gly Lys Lys Phe Leu Val Pro Val Asn 2435 2440 2445 Pro Glu Asn Gly Arg Val Gln Trp Glu Ala Ala Lys Leu Ser Val Glu 2450 2455 2460 Gln Ala Leu Gly Met Met Asn Val Asp Gly Glu Leu Thr Ala Lys Glu 2465 2470 2475 2480 Leu Glu Lys Leu Lys Arg Ile Ile Asp Lys Leu Gln Gly Leu Thr Lys 2485 2490 2495 Glu Gln Cys Leu Asn Cys 2500 2 1457 PRT Porcine reproductive and respiratory syndrome virus 2 Leu Ala Ala Ser Asp Leu Thr Arg Cys Gly Arg Gly Gly Leu Val Val 1 5 10 15 Thr Glu Thr Ala Val Lys Ile Val Lys Phe His Asn Arg Thr Phe Thr 20 25 30 Leu Gly Pro Val Asn Leu Lys Val Ala Ser Glu Val Glu Leu Lys Asp 35 40 45 Ala Val Glu His Asn Gln His Pro Val Ala Arg Pro Ile Asp Gly Gly 50 55 60 Val Val Leu Leu Arg Ser Ala Val Pro Ser Leu Ile Asp Val Leu Ile 65 70 75 80 Ser Gly Ala Asp Ala Ser Pro Lys Leu Leu Ala His His Gly Pro Gly 85 90 95 Asn Thr Gly Ile Asp Gly Thr Leu Trp Asp Phe Glu Ser Glu Ala Thr 100 105 110 Lys Glu Glu Val Ala Leu Ser Ala Gln Ile Ile Gln Ala Cys Asp Ile 115 120 125 Arg Arg Gly Asp Ala Pro Glu Ile Gly Leu Pro Tyr Lys Leu Tyr Pro 130 135 140 Val Arg Gly Asn Pro Glu Arg Val Lys Gly Val Leu Gln Asn Thr Arg 145 150 155 160 Phe Gly Asp Ile Pro Tyr Lys Thr Pro Ser Asp Thr Gly Ser Pro Val 165 170 175 His Ala Ala Ala Cys Leu Thr Pro Asn Ala Thr Pro Val Thr Asp Gly 180 185 190 Arg Ser Val Leu Ala Thr Thr Met Pro Pro Gly Phe Glu Leu Tyr Val 195 200 205 Pro Thr Ile Pro Ala Ser Val Leu Asp Tyr Leu Asp Ser Arg Pro Asp 210 215 220 Cys Pro Lys Gln Leu Thr Glu His Gly Cys Glu Asp Ala Ala Leu Lys 225 230 235 240 Asp Leu Ser Lys Tyr Asp Leu Ser Thr Gln Gly Phe Val Leu Pro Gly 245 250 255 Val Leu Arg Leu Val Arg Lys Tyr Leu Phe Ala His Val Gly Lys Cys 260 265 270 Pro Pro Val His Arg Pro Ser Thr Tyr Pro Ala Lys Asn Ser Met Ala 275 280 285 Gly Ile Asn Gly Asn Arg Phe Pro Thr Lys Asp Ile Gln Ser Val Pro 290 295 300 Glu Ile Asp Val Leu Cys Ala Gln Ala Val Arg Glu Asn Trp Gln Thr 305 310 315 320 Val Thr Pro Cys Thr Leu Lys Lys Gln Tyr Cys Gly Lys Lys Lys Thr 325 330 335 Arg Thr Ile Leu Gly Thr Asn Asn Phe Ile Ala Leu Ala His Arg Ala 340 345 350 Val Leu Ser Gly Val Thr Gln Gly Phe Met Lys Lys Ala Phe Asn Ser 355 360 365 Pro Ile Ala Leu Gly Lys Asn Lys Phe Lys Glu Leu Gln Thr Pro Val 370 375 380 Leu Gly Arg Cys Leu Glu Ala Asp Leu Ala Ser Cys Asp Arg Ser Thr 385 390 395 400 Pro Ala Ile Val Arg Trp Phe Ala Ala Asn Leu Leu Tyr Glu Leu Ala 405 410 415 Cys Ala Glu Glu His Leu Pro Ser Tyr Val Leu Asn Cys Cys His Asp 420 425 430 Leu Leu Val Thr Gln Ser Gly Ala Val Thr Lys Arg Gly Gly Leu Ser 435 440 445 Ser Gly Asp Pro Ile Thr Ser Val Ser Asn Thr Ile Tyr Ser Leu Val 450 455 460 Ile Tyr Ala Gln His Met Val Leu Ser Tyr Phe Lys Ser Gly His Pro 465 470 475 480 His Gly Leu Leu Phe Leu Gln Asp Gln Leu Lys Phe Glu Asp Met Leu 485 490 495 Lys Val Gln Pro Leu Ile Val Tyr Ser Asp Asp Leu Val Leu Tyr Ala 500 505 510 Glu Ser Pro Thr Met Pro Asn Tyr His Trp Trp Val Glu His Leu Asn 515 520 525 Leu Met Leu Gly Phe Gln Thr Asp Pro Lys Lys Thr Ala Ile Thr Asp 530 535 540 Ser Pro Ser Phe Leu Gly Cys Arg Ile Ile Asn Gly Arg Gln Leu Val 545 550 555 560 Pro Asn Arg Asp Arg Ile Leu Ala Ala Leu Ala Tyr His Met Lys Ala 565 570 575 Ser Asn Val Ser Glu Tyr Tyr Ala Ser Ala Ala Ala Ile Leu Met Asp 580 585 590 Ser Cys Ala Cys Leu Glu Tyr Asp Pro Glu Trp Phe Glu Glu Leu Val 595 600 605 Val Gly Ile Ala Gln Cys Ala Arg Lys Asp Gly Tyr Ser Phe Pro Gly 610 615 620 Thr Pro Phe Phe Met Ser Met Trp Glu Lys Leu Arg Ser Asn Tyr Glu 625 630 635 640 Gly Lys Lys Ser Arg Val Cys Gly Tyr Cys Gly Ala Pro Ala Pro Tyr 645 650 655 Ala Thr Ala Cys Gly Leu Asp Val Cys Ile Tyr His Thr His Phe His 660 665 670 Gln His Cys Pro Val Thr Ile Trp Cys Gly His Pro Ala Gly Ser Gly 675 680 685 Ser Cys Ser Glu Cys Lys Ser Pro Val Gly Lys Gly Thr Ser Pro Leu 690 695 700 Asp Glu Val Leu Glu Gln Val Pro Tyr Lys Pro Pro Arg Thr Val Ile 705 710 715 720 Met His Val Glu Gln Gly Leu Thr Pro Leu Asp Pro Gly Arg Tyr Gln 725 730 735 Thr Arg Arg Gly Leu Val Ser Val Arg Arg Gly Ile Arg Gly Asn Glu 740 745 750 Val Gly Leu Pro Asp Gly Asp Tyr Ala Ser Thr Ala Leu Leu Pro Thr 755 760 765 Cys Lys Glu Ile Asn Met Val Ala Val Ala Ser Asn Val Leu Arg Ser 770 775 780 Arg Phe Ile Ile Gly Pro Pro Gly Ala Gly Lys Thr Tyr Trp Leu Leu 785 790 795 800 Gln Gln Val Gln Asp Gly Asp Val Ile Tyr Thr Pro Thr His Gln Thr 805 810 815 Met Leu Asp Met Ile Arg Ala Leu Gly Thr Cys Arg Phe Asn Val Pro 820 825 830 Ala Gly Thr Thr Leu Gln Phe Pro Val Pro Ser Arg Thr Gly Pro Trp 835 840 845 Val Arg Ile Leu Ala Gly Gly Trp Cys Pro Gly Lys Asn Ser Phe Leu 850 855 860 Asp Glu Ala Ala Tyr Cys Asn His Leu Asp Val Leu Arg Leu Leu Ser 865 870 875 880 Lys Thr Thr Leu Thr Cys Leu Gly Asp Phe Lys Gln Leu His Pro Val 885 890 895 Gly Phe Asp Ser His Cys Tyr Val Phe Asp Ile Met Pro Gln Thr Gln 900 905 910 Leu Lys Thr Ile Trp Arg Phe Gly Gln Asn Ile Cys Asp Ala Ile Gln 915 920 925 Pro Asp Tyr Arg Asp Lys Leu Met Ser Met Val Asn Thr Thr Arg Val 930 935 940 Thr Tyr Val Glu Lys Pro Val Arg Tyr Gly Gln Val Leu Thr Pro Tyr 945 950 955 960 His Arg Asp Arg Glu Asp Asp Ala Ile Thr Ile Asp Ser Ser Gln Gly 965 970 975 Ala Thr Phe Asp Val Val Thr Leu His Leu Pro Thr Lys Asp Ser Leu 980 985 990 Asn Arg Gln Arg Ala Leu Val Ala Ile Thr Arg Ala Arg His Ala Ile 995 1000 1005 Phe Val Tyr Asp Pro His Arg Gln Leu Gln Gly Leu Phe Asp Leu Pro 1010 1015 1020 Ala Lys Gly Thr Pro Val Asn Leu Ala Val His Cys Asp Gly Gln Leu 1025 1030 1035 1040 Ile Val Leu Asp Arg Asn Asn Lys Glu Cys Thr Val Ala Gln Ala Leu 1045 1050 1055 Gly Asn Gly Asp Lys Phe Arg Ala Thr Asp Lys Arg Val Val Asp Ser 1060 1065 1070 Leu Arg Ala Ile Cys Ala Asp Leu Glu Gly Ser Ser Ser Pro Leu Pro 1075 1080 1085 Lys Val Ala His Asn Leu Gly Phe Tyr Phe Ser Pro Asp Leu Thr Gln 1090 1095 1100 Phe Ala Lys Leu Pro Val Glu Leu Ala Pro His Trp Pro Val Val Ser 1105 1110 1115 1120 Thr Gln Asn Asn Glu Lys Trp Pro Asp Arg Leu Val Ala Ser Leu Arg 1125 1130 1135 Pro Ile His Lys Tyr Ser Arg Ala Cys Ile Gly Ala Gly Tyr Met Val 1140 1145 1150 Gly Pro Ser Val Phe Leu Gly Thr Pro Gly Val Val Ser Tyr Tyr Leu 1155 1160 1165 Thr Lys Phe Val Lys Gly Gly Ala Gln Val Leu Pro Glu Thr Val Phe 1170 1175 1180 Ser Thr Gly Arg Ile Glu Val Asp Cys Arg Glu Tyr Leu Asp Asp Arg 1185 1190 1195 1200 Glu Arg Glu Val Ala Ala Ser Leu Pro His Gly Phe Ile Gly Asp Val 1205 1210 1215 Lys Gly Thr Thr Val Gly Gly Cys His His Val Thr Ser Arg Tyr Leu 1220 1225 1230 Pro Arg Val Leu Pro Lys Glu Ser Val Ala Val Val Gly Val Ser Ser 1235 1240 1245 Pro Gly Lys Ala Ala Lys Ala Leu Cys Thr Leu Thr Asp Val Tyr Leu 1250 1255 1260 Pro Asp Leu Glu Ala Tyr Leu His Pro Glu Thr Gln Ser Lys Cys Trp 1265 1270 1275 1280 Lys Met Met Leu Asp Phe Lys Glu Val Arg Leu Met Val Trp Lys Asp 1285 1290 1295 Lys Thr Ala Tyr Phe Gln Leu Glu Gly Arg Tyr Phe Thr Trp Tyr Gln 1300 1305 1310 Leu Ala Ser Tyr Ala Ser Tyr Ile Arg Val Pro Val Asn Ser Thr Val 1315 1320 1325 Tyr Leu Asp Pro Cys Met Gly Pro Ala Leu Cys Asn Arg Arg Val Val 1330 1335 1340 Gly Ser Thr His Trp Gly Ala Asp Leu Ala Val Thr Pro Tyr Asp Tyr 1345 1350 1355 1360 Gly Ala Lys Ile Ile Leu Ser Ser Ala Tyr His Gly Glu Met Pro Pro 1365 1370 1375 Gly Tyr Lys Ile Leu Ala Cys Ala Glu Phe Ser Leu Asp Asp Pro Val 1380 1385 1390 Lys Tyr Lys His Thr Trp Gly Phe Glu Ser Asp Thr Ala Tyr Leu Tyr 1395 1400 1405 Glu Phe Thr Gly Asn Gly Glu Asp Trp Glu Asp Tyr Asn Asp Ala Phe 1410 1415 1420 Arg Ala Arg Gln Glu Gly Lys Ile Tyr Lys Ala Thr Ala Thr Ser Leu 1425 1430 1435 1440 Lys Phe Tyr Phe Pro Pro Gly Pro Val Ile Glu Pro Thr Leu Gly Leu 1445 1450 1455 Asn 3 256 PRT Porcine reproductive and respiratory syndrome virus 3 Met Lys Trp Gly Pro Cys Lys Ala Phe Leu Thr Lys Leu Ala Asn Phe 1 5 10 15 Leu Trp Met Leu Ser Arg Ser Ser Trp Cys Pro Leu Leu Ile Ser Leu 20 25 30 Tyr Phe Trp Pro Phe Cys Leu Ala Ser Pro Ser Pro Val Gly Trp Trp 35 40 45 Ser Phe Ala Ser Asp Trp Phe Ala Pro Arg Tyr Ser Val Arg Ala Leu 50 55 60 Pro Phe Thr Leu Ser Asn Tyr Arg Arg Ser Tyr Glu Ala Phe Leu Ser 65 70 75 80 Gln Cys Gln Val Asp Ile Pro Thr Trp Gly Thr Lys His Pro Leu Gly 85 90 95 Met Leu Trp His His Lys Val Ser Thr Leu Ile Asp Glu Met Val Ser 100 105 110 Arg Arg Met Tyr Arg Ile Met Glu Lys Ala Gly Gln Ala Ala Trp Lys 115 120 125 Gln Val Val Ser Glu Ala Thr Leu Ser Arg Ile Ser Ser Leu Asp Val 130 135 140 Val Ala His Phe Gln His Leu Ala Ala Ile Glu Ala Glu Thr Cys Lys 145 150 155 160 Tyr Leu Ala Ser Arg Leu Pro Met Leu His Asn Leu Arg Met Thr Gly 165 170 175 Ser Asn Val Thr Ile Val Tyr Asn Ser Thr Leu Asn Gln Val Phe Ala 180 185 190 Ile Phe Pro Thr Pro Gly Ser Arg Pro Lys Leu His Asp Phe Gln Gln 195 200 205 Trp Leu Ile Ala Val His Ser Ser Ile Phe Ser Ser Val Ala Ala Ser 210 215 220 Cys Thr Leu Phe Val Val Leu Trp Leu Arg Val Pro Ile Leu Arg Thr 225 230 235 240 Val Phe Gly Phe Arg Trp Leu Gly Ala Ile Phe Leu Ser Asn Ser Gln 245 250 255 4 7509 DNA Porcine reproductive and respiratory syndrome virus 4 atgtctggga tacttgatcg gtgcacgtgt acccccaatg ccagggtgtt tatggcggag 60 ggccaagtct actgcacacg atgcctcagt gcacggtctc tccttcccct gaacctccaa 120 gtttctgagc tcggggtgct aggcctattc tacaggcccg aagagccact ccggtggacg 180 ttgccacgtg cattccccac tgttgagtgc tcccccgccg gggcctgctg gctttctgca 240 atctttccaa tcgcacgaat gaccagtgga aacctgaact tccaacaaag aatggtacgg 300 gtcgcagctg agctttacag agccggccag ctcacccctg cagtcttgaa ggctctacaa 360 gtttatgaac ggggttgccg ctggtacccc attgttggac ctgtccctgg agtggccgtt 420 ttcgccaatt ccctacatgt gagtgataaa cctttcccgg gagcaactca cgtgttgacc 480 aacctgccgc tcccgcagag acccaagcct gaagactttt gcccctttga gtgtgctatg 540 gctactgtct atgacattgg tcatgacgcc gtcatgtatg tggccgaaag gaaagtctcc 600 tgggcccctc gtggcgggga tgaagtgaaa tttgaagctg tccccgggga gttgaagttg 660 attgcgaacc ggctccgcac ctccttcccg ccccaccaca cagtggacat gtctaagttc 720 gccttcacag cccctgggtg tggtgtttct atgcgggtcg aacgccaaca cggctgcctt 780 cccgctgaca ctgtccctga aggcaactgc tggtggagct tgtttgactt gcttccactg 840 gaagttcaga acaaagaaat tcgccatgct aaccaatttg gctaccagac caagcatggt 900 gtctctggca agtacctaca gcggaggctg caagttaatg gtctccgagc agtaactgac 960 ctaaacggac ctatcgtcgt acagtacttc tccgttaagg agagttggat ccgccatttg 1020 aaactggcgg gagaacccag ctactctggg tttgaggacc tcctcagaat aagggttgag 1080 cctaacacgt cgccattggc tgacaaggaa gaaaaaattt tccggtttgg cagtcacaag 1140 tggtacggcg ctggaaagag agcaagaaaa gcacgctctt gtgcgactgc tacagtcgct 1200 ggccgcgctt tgtccgttcg tgaaacccgg caggccaagg agcacgaggt tgccggcgcc 1260 aacaaggctg agcacctcaa acactactcc ccgcctgccg aagggaattg tggttggcac 1320 tgcatttccg ccatcgccaa ccggatggtg aattccaaat ttgaaaccac ccttcccgaa 1380 agagtgagac ctccagatga ctgggctact gacgaggatc ttgtgaatgc catccaaatc 1440 ctcagactcc ctgcggcctt agacaggaac ggtgcttgta ctagcgccaa gtacgtactt 1500 aagctggaag gtgagcattg gactgtcact gtgacccctg ggatgtcccc ttctttgctc 1560 cctcttgaat gtgttcaggg ctgttgtggg cacaagggcg gtcttggttc cccagatgca 1620 gtcgaggtct ccggatttga ccctgcctgc cttgaccggc tggctgaggt gatgcacctg 1680 cctagcagtg ctatcccagc cgctctggcc gaaatgtctg gcgattccga tcgttcggct 1740 tctccggtca ccaccgtgtg gactgtttcg cagttctttg cccgtcacag cggagggaat 1800 caccctgacc aagtgcgctt agggaaaatt atcagccttt gtcaggtgat tgaggactgc 1860 tgctgttccc agaacaaaac caaccgggtc accccggagg aggtcgcagc aaagattgac 1920 ctgtacctcc gtggtgcaac aaatcttgaa gaatgcttgg ccaggcttga gaaagcgcgc 1980 ccgccacgcg taatcgacac ctcctttgat tgggatgttg tgctccctgg ggttgaggcg 2040 gcaacccaga cgatcaagct gccccaggtc aaccagtgtc gtgctctggt ccctgttgtg 2100 actcaaaagt ccttggacaa caactcggtc cccctgaccg ccttttcact ggctaactac 2160 tactaccgtg cgcaaggtga cgaagttcgt caccgtgaaa gactaaccgc cgtgctctcc 2220 aagttggaaa aggttgttcg agaagaatat gggctcatgc caaccgagcc tggtccacgg 2280 cccacactgc cacgcgggct cgacgaactc aaagaccaga tggaggagga cttgctgaaa 2340 ctggctaacg cccagacgac ttcggacatg atggcctggg cagtcgagca ggttgaccta 2400 aaaacttggg tcaagaacta cccgcggtgg acaccaccac cccctccgcc aaaagttcag 2460 cctcgaaaaa cgaagcctgt caagagcttg ccggagagaa agcctgtccc cgccccgcgc 2520 aggaaggttg ggtccgattg tggcagcccg gtttcattag gcggcgatgt ccctaacagt 2580 tgggaagatt tggctgttag tagccccttt gatctcccga ccccacctga gccggcaaca 2640 ccttcaagtg agctggtgat tgtgtcctca ccgcaatgca tcttcaggcc ggcgacaccc 2700 ttgagtgagc cggctccaat tcccgcacct cgcggaactg tgtctcgacc ggtgacaccc 2760 ttgagtgagc cgatccctgt gcccgcaccg cggcgtaagt ttcagcaggt gaaaagattg 2820 agttcggcgg cggcaatccc accgtaccag gacgagcccc tggatttgtc tgcttcctca 2880 cagactgaat atgaggcctc tcccccagca ccgccgcaga gcgggggcgt tctgggagta 2940 gaggggcatg aagctgagga aaccctgagt gaaatctcgg acatgtcggg taacattaaa 3000 cctgcgtccg tgtcatcaag cagctccttg tccagcgtga gaatcacacg cccaaaatac 3060 tcagctcaag ccatcatcga ctcgggcggg ccctgcagtg ggcatctcca agaggtaaag 3120 gaaacatgcc ttagtgtcat gcgcgaggca tgtgatgcga ctaagcttga tgaccctgct 3180 acgcaggaat ggctttctcg catgtgggat cgggtggaca tgctgacttg gcgcaacacg 3240 tctgtttacc aggcgatttg caccttagat ggcaggttaa agttcctccc aaaaatgata 3300 ctcgagacac cgccgcccta tccgtgtgag tttgtgatga tgcctcacac gcctgcacct 3360 tccgtaggtg cggagagcga ccttaccatt ggctcagttg ctactgaaga tgttccacgc 3420 atcctcgaga aaatagaaaa tgtcggcgag atggccaacc agggaccctt ggccttctcc 3480 gaggataaac cggtagatga ccaacttgtc aacgaccccc ggatatcgtc gcggaggcct 3540 gacgagagca catcagctcc gtccgcaggc acaggtggcg ccggctcttt taccgatttg 3600 ccgccttcag atggcgcgga tgcggacggg ggggggccgt ttcggacggt aaaaagaaaa 3660 gctgaaaggc tctttgacca actgagccgt caggtttttg acctcgtctc ccatctccct 3720 gttttcttct cacgcctttt ctaccctggc ggtggttatt ctccgggtga ttggggtttt 3780 gcagctttta ctctattgtg cctcttttta tgttacagtt acccagcctt tggtattgct 3840 cccctcttgg gtgtgttttc tgggtcttct cggcgcgttc gaatgggggt ttttggctgc 3900 tggttggctt ttgctgttgg tctgttcaag cctgtgtccg acccagtcgg cgctgcttgt 3960 gagtttgact cgccagagtg tagaaacatc cttcattctt ttgagcttct caaaccttgg 4020 gaccctgttc gcagccttgt tgtgggcccc gtcggtctcg gtcttgccat tcttggcagg 4080 ttactgggcg gggcacgctg catctggcac tttttgctta ggcttggcat tgttgcagac 4140 tgtatcttgg ctggagctta cgtgctttct caaggtaggt gtaaaaagtg ctggggatct 4200 tgtataagaa ctgctcctaa tgaggtcgct tttaacgtgt ttcctttcac acgtgcgacc 4260 aggtcgtcac ttatcgacct gtgcgatcgg ttttgtgcgc caaaaggaat ggaccccatt 4320 tttctcgcca ctgggtggcg cgggtgctgg gccggccgaa gccccattga gcaaccctct 4380 gaaaaaccca tcgcgtttgc ccaattggat gaaaagaaga ttacggctag gactgtggtc 4440 gcccagcctt atgaccccaa ccaagccgta aagtgcttgc gggtattgca gtcgggtggg 4500 cgatggtggc taagcggtcc caaaagtggt caaggtttcc gctgttccat tccgagcccc 4560 ttctttccca ctggagtgaa agttgaccct gattgcaggg tcgtggttga ccctgacact 4620 ttcactgcag ctctccggtc tggctactcc accacaaacc tcgtccttgg tgtaggggac 4680 tttgcccagc tgaatggatt aaaaatcagg caaatttcca agccttcagg gggaggccca 4740 catctcatgg ctgccctgca tgttgcctgc tcgatggctc tgcacatgct tgctgggatt 4800 tatgtgactg cggtgggttc ttgcggcacc ggcaccaacg acccgtggtg cgctaacccg 4860 tttgccgtcc ctggctacgg acctggctct ctctgcacgt ccaggttgtg catttcccaa 4920 cacggcctta ccctgccctt gacagcactt gtggcgggat tcggtattca agaaattgcc 4980 ttggtcgttt tgatttttgt ttccatcgga ggcatggctc ataggttgag ctgtaaggct 5040 gacatgctgt gtgttttgct tgcaattgcc agctatgttt gggtacctct tacctggttg 5100 ctttgtgtgt ttccttgctg gttgcgctgt ttttctttgc accccctcac catcctatgg 5160 ttggtgtttt tcttgatttc tgtgaatatg ccttcaggaa tcttggccat ggtgttgttg 5220 gtttctcttt ggcttcttgg tcgttatact aatgttgctg gccttgtcac cccctacgac 5280 attcatcatt acaccagtgg cccccgcggt gttgccgcct tggctaccgc accagatggg 5340 acctacttgg ccgctgtccg ccgcgctgcg ttgactggcc gcaccatgct gtttaccccg 5400 tcccagcttg ggtctcttct tgagggtgct ttcagaactc gaaagccctc actgaacacc 5460 gtcaatgtga tcgggtcctc catgggctct ggcggggtgt ttaccatcga cgggaaagtc 5520 aagtgcgtaa ctgccgcaca tgtccttacg ggcaattcag ctcgggtttc cggggtcggc 5580 ttcaatcaaa tgcttgactt tgacgtaaag ggagatttcg ctatagctga ttgcccgaat 5640 tggcaagggg ctgcccccaa gacccaattc tgcacggatg gatggactgg ccgtgcctat 5700 tggctaacat cctctggcgt cgaacccggc gtcattggaa aaggattcgc cttctgcttc 5760 accgcatgtg gcgattccgg gtccccagtg atcaccgagg ccggtgagct tgtcggcgtt 5820 cacacgggat cgaataaaca aggggggggc attgttacgc gcccctcagg ccagttttgt 5880 aatgtggcac ccatcaagct aagcgaatta agtgaattct ttgctgggcc taaggtcccg 5940 ctcggtgatg tgaaggtcgg cagccacata attaaagaca taagcgaggt gccttcagat 6000 ctttgtgcct tgcttgctgc caaacctgaa ctggaaggag gcctctccac cgtccaactt 6060 ctttgtgtgt tttttctcct gtggagaatg atgggacatg cctggacgcc cttggttgct 6120 gtgagtttct ttattttgaa tgaggttctc ccagccgtcc tggtccggag tgttttctcc 6180 tttggaatgt ttgtgctatc ctggctcacg ccatggtctg cgcaagttct gatgatcagg 6240 cttctgacag cagctcttaa caggaacaga tggtcacttg cctttttcag cctcggtgca 6300 gtgaccggtt ttgtcgcaga tcttgcggcc actcaggggc atccgttgca ggcagtgatg 6360 aatttgagca cctatgcatt cctgcctcgg atgatggttg tgacctcacc agtcccagtg 6420 atcacgtgtg gtgtcgtgca cctacttgcc atcattttgt acttgtttaa gtaccgtggc 6480 ccgcaccata tccttgttgg cgatggagtg ttctctgcgg ctttcttctt gagatacttt 6540 gccgagggaa agttgaggga aggggtgtcg caatcctgcg gaatgaatca tgagtctctg 6600 actggtgccc tcgctatgag actcaatgac gaggacttgg atttccttat gaaatggact 6660 gattttaagt gctttgtttc tgcgtccaac atgaggaatg cagcgggtca atttatcgag 6720 gctgcctatg ctaaagcact tagagtagaa ctggcccagt tggtgcaggt tgataaagtt 6780 cgaggtactt tggccaaact tgaagctttt gctgataccg tggcacctca actctcgccc 6840 ggtgacattg ttgtcgctct cggccacacg cctgttggca gtatcttcga cctaaaggtt 6900 ggtagcacca agcataccct ccaagccatt gagaccagag tccttgctgg gtccaaaatg 6960 accgtggcgc gcgtcgtcga cccgaccccc acgcccccac ccgcacccgt gcccatcccc 7020 ctcccaccga aagttctgga gaatggcccc aacgcttggg gggatgagga ccgtttgaat 7080 aagaagaaga ggcgcaggat ggaagccctc ggcatctatg ttatgggcgg gaaaaagtac 7140 cagaaatttt gggacaagaa ttccggtgat gtgttttatg aggaggtcca taataacaca 7200 gatgagtggg agtgtctcag agttggcgac cctgccgact ttgaccctga gaagggaact 7260 ctgtgtggac atgtcaccat tgaaaacaag gcttaccatg tttacacctc cccatctggt 7320 aagaagttct tggtccccgt caacccagag aatggaagag ttcaatggga agctgcaaag 7380 ctttccgtgg agcaggccct aggtatgatg aatgtcgacg gcgaactgac tgccaaagaa 7440 ctggagaaac tgaaaagaat aattgacaaa ctccagggcc tgactaagga gcagtgttta 7500 aactgctag 7509 5 4374 DNA Porcine reproductive and respiratory syndrome virus 5 ctagccgcca gcgacttgac ccgctgtggt cgcggcggct tggttgttac tgaaacagcg 60 gtaaaaatag tcaaatttca caaccggacc ttcaccctgg gacctgtgaa tttaaaagtg 120 gccagtgagg ttgagctaaa agacgcggtt gagcacaacc aacacccggt tgcgagaccg 180 atcgatggtg gagttgtgct cctgcgttcc gcggttcctt cgcttataga cgtcttgatc 240 tccggtgctg atgcatctcc caagttactt gcccatcacg ggccgggaaa cactgggatc 300 gatggcacgc tctgggattt tgagtccgaa gccactaaag aggaagtcgc actcagtgcg 360 caaataatac aggcttgtga cattaggcgc ggcgacgctc ctgaaattgg tctcccttac 420 aagctgtacc ctgttagggg taaccctgag cgggtgaaag gagttctgca gaatacaagg 480 tttggagaca taccttacaa aacccccagt gacactggaa gcccagtgca cgcggctgcc 540 tgccttacgc ccaacgccac tccggtgact gatgggcgct ccgtcttggc cacgaccatg 600 ccccccgggt ttgagttata tgtaccgacc ataccagcgt ctgtccttga ttaccttgac 660 tctaggcctg actgccctaa acagctgaca gagcacggct gcgaagatgc cgcactgaaa 720 gacctctcta aatatgactt gtccacccaa ggctttgttt tacctggagt tcttcgcctt 780 gtgcggaaat acctgtttgc ccatgtaggt aagtgcccac ccgttcatcg gccttctact 840 taccctgcta agaattctat ggctggaata aatgggaaca ggttcccaac caaggacatt 900 cagagcgtcc ctgaaatcga cgttctgtgc gcacaggctg tgcgagaaaa ctggcaaact 960 gtcacccctt gtactcttaa gaaacagtat tgcgggaaga agaagactag gaccatactc 1020 ggcaccaata acttcatcgc actagcccac cgagcagtgt tgagtggtgt tacccagggc 1080 ttcatgaaaa aggcgtttaa ctcgcccatc gccctcggaa agaacaagtt taaggagcta 1140 cagactccgg tcctgggcag gtgccttgaa gctgatctcg catcctgcga tcgatccacg 1200 cctgcaattg tccgctggtt tgccgccaac cttctttatg aacttgcctg tgctgaagag 1260 catctaccgt cgtacgtgct gaactgctgc cacgacttac tggtcacgca gtccggcgca 1320 gtgactaaga gaggtggcct gtcgtctggc gacccgatca cctctgtgtc taacaccatt 1380 tatagtttgg tgatctatgc acagcatatg gtgcttagtt acttcaaaag tggtcacccc 1440 catggccttc tgttcttaca agaccagcta aagtttgagg acatgctcaa ggttcaaccc 1500 ctgatcgtct attcggacga cctcgtgctg tatgccgagt ctcccaccat gccaaactat 1560 cactggtggg ttgaacatct gaatttgatg ctggggtttc agacggaccc aaagaagaca 1620 gcaataacag actcgccatc atttctaggc tgtagaataa taaatgggcg ccagctagtc 1680 cccaaccgtg acaggatcct cgcggccctc gcctatcaca tgaaggcgag taatgtttct 1740 gaatactatg cctcagcggc tgcaatactc atggacagct gtgcttgttt ggagtatgat 1800 cctgaatggt ttgaagaact tgtagttgga atagcgcagt gcgcccgcaa ggacggctac 1860 agctttcccg gcacgccgtt cttcatgtcc atgtgggaaa aactcaggtc caattatgag 1920 gggaagaagt cgagagtgtg cgggtactgc ggggccccgg ccccgtacgc tactgcctgt 1980 ggcctcgacg tctgcattta ccacacccac ttccaccagc attgtccagt cacaatctgg 2040 tgtggccatc cagcgggttc tggttcttgt agtgagtgca aatcccctgt agggaaaggc 2100 acaagccctt tagacgaggt gctggaacaa gtcccgtata agcccccacg gaccgttatc 2160 atgcatgtgg agcagggtct cacccccctt gatccaggta gataccaaac tcgccgcgga 2220 ttagtctctg tcaggcgtgg aattagggga aatgaagttg gactaccaga cggtgattat 2280 gctagcaccg ccttgctccc tacctgcaaa gagatcaaca tggtcgctgt cgcttccaat 2340 gtattgcgca gcaggttcat catcggccca cccggtgctg ggaaaacata ctggctcctt 2400 caacaggtcc aggatggtga tgttatttac acaccaactc accagaccat gcttgacatg 2460 attagggctt tggggacgtg ccggttcaac gtcccggcag gcacaacgct gcaattcccc 2520 gtcccctccc gcaccggtcc gtgggttcgc atcctagccg gcggttggtg tcctggcaag 2580 aattccttcc tagatgaagc agcgtattgc aatcaccttg atgttttgag gcttcttagt 2640 aaaactaccc tcacctgtct aggagacttc aagcaactcc acccagtggg ttttgattct 2700 cattgctatg tttttgacat catgcctcaa actcaactga agaccatctg gaggtttgga 2760 cagaatatct gtgatgccat tcagccagat tacagggaca aactcatgtc catggtcaac 2820 acaacccgtg tgacctacgt ggaaaaacct gtcaggtatg ggcaggtcct caccccctac 2880 cacagggacc gagaggacga cgccatcact attgactcca gtcaaggcgc cacattcgat 2940 gtggttacat tgcatttgcc cactaaagat tcactcaaca ggcaaagagc ccttgttgct 3000 atcaccaggg caagacacgc tatctttgtg tatgacccac acaggcagct gcagggcttg 3060 tttgatcttc ctgcaaaagg cacgcccgtc aacctcgcag tgcactgcga cgggcagctg 3120 atcgtgctgg atagaaataa caaagaatgc acggttgctc aggctctagg caacggggat 3180 aaatttaggg ccacagacaa gcgtgttgta gattctctcc gcgccatttg tgctgatcta 3240 gaagggtcga gctctccgct ccccaaggtc gcacacaact tgggatttta tttctcacct 3300 gatttaacac agtttgctaa actcccagta gaacttgcac ctcactggcc cgtggtgtca 3360 acccagaaca atgaaaagtg gccggatcgg ctggttgcca gccttcgccc tatccataaa 3420 tacagccgcg cgtgcatcgg tgccggctat atggtgggcc cttcggtgtt tctaggcact 3480 cctggggtcg tgtcatacta tctcacaaaa tttgttaagg gcggggctca agtgcttccg 3540 gagacggttt tcagcaccgg ccgaattgag gtagactgcc gggaatatct tgatgatcgg 3600 gagcgagaag ttgctgcgtc cctcccacac ggtttcattg gcgacgtcaa aggcactacc 3660 gttggaggat gtcatcatgt cacctccaga tacctcccgc gcgtccttcc caaggaatca 3720 gttgcggtag tcggggtttc aagccccgga aaagccgcga aagcattgtg cacactgaca 3780 gatgtgtacc tcccagatct tgaagcctat ctccacccgg agacccagtc caagtgctgg 3840 aaaatgatgt tggacttcaa agaagttcga ctaatggtct ggaaagacaa aacagcctat 3900 ttccaacttg aaggtcgcta tttcacctgg tatcagcttg ccagctatgc ctcgtacatc 3960 cgtgttcccg tcaactctac ggtgtacttg gacccctgca tgggccccgc cctttgcaac 4020 aggagagtcg tcgggtccac ccactggggg gctgacctcg cggtcacccc ttatgattac 4080 ggcgctaaaa ttatcctgtc tagcgcgtac catggtgaaa tgccccccgg atacaaaatt 4140 ctggcgtgcg cggagttctc gttggatgac ccagttaagt acaaacatac ctgggggttt 4200 gaatcggata cagcgtatct gtatgagttc accggaaacg gtgaggactg ggaggattac 4260 aatgatgcgt ttcgtgcgcg ccaggaaggg aaaatttata aggccactgc caccagcttg 4320 aagttttatt ttcccccggg ccctgtcatt gaaccaactt taggcctgaa ttga 4374 6 771 DNA Porcine reproductive and respiratory syndrome virus 6 atgaaatggg gtccatgcaa agcctttttg acaaaattgg ccaacttttt gtggatgctt 60 tcacggagtt cttggtgtcc attgttgata tcattatatt tttggccatt ttgtttggct 120 tcaccatcgc cggttggctg gtggtctttt gcatcagatt ggtttgctcc gcgatactcc 180 gtacgcgccc tgccattcac tctgagcaat tacagaagat cttatgaggc ctttctttcc 240 cagtgccaag tggacattcc cacctgggga actaaacatc ctttggggat gctttggcac 300 cataaggtgt caaccctgat tgatgaaatg gtgtcgcgtc gaatgtaccg catcatggaa 360 aaagcagggc aggctgcctg gaaacaggtg gtgagcgagg ctacgctgtc tcgcattagt 420 agtttggatg tggtggctca ttttcagcat ctagccgcca ttgaagccga gacctgtaaa 480 tatttggcct cccggctgcc catgctacac aacctgcgca tgacagggtc aaatgtaacc 540 atagtgtata atagcacttt gaatcaggtg tttgctattt ttccaacccc tggttcccgg 600 ccaaagcttc atgattttca gcaatggtta atagctgtac attcctccat attttcctct 660 gttgcagctt cttgtactct ttttgttgtg ctgtggttgc gggttccaat actacgtact 720 gtttttggtt tccgctggtt aggggcaatt tttctttcga actcacagtg a 771 

what is claimed is:
 1. A live attenuated PRRS virus comprising ORF 1 a , 1 b and 2 essentially as in ATCC VR-2332, wherein said virus is not ATCC VR-2495, and wherein at least one of the amino acids in position 321 to 341 encoded by ORF 1 a is not identical to the amino acid(s) of ATCC VR 2332 at the corresponding position(s) and/or at least one of the amino acids in position 936 to 956 encoded by ORF 1 b is not identical to the amino acid(s) of the strain VR 2332 at the corresponding position(s) and/or at least one of the amino acids in position 1 to 20 encoded by ORF 2 is not identical to the amino acid(s) of ATCC VR 2332 at the corresponding position(s), and wherein said live attenuated PRRS virus is less virulent than ATCC VR-2332.
 2. The live attenuated PRRS virus according to claim 1, wherein at least one of the amino acids in position 321 to 341 encoded by ORF 1 a is deleted and/or at least one of the amino acids in position 936 to 956 encoded by ORF 1 b is deleted and/or at least one of the amino acids in position 1 to 20 encoded by ORF 2 is deleted.
 3. The live attenuated PRRS virus according to claim 1, wherein the amino acid in position 331 encoded by ORF 1 a and/or the amino acid in position 946 encoded by ORF 1 b and/or the amino acid in position 10 encoded by ORF 2 is/are not identical to the amino acid(s) of ATCC VR-2332 at the corresponding position(s).
 4. The live attenuated PRRS virus according to claim 2 wherein the amino acid in position 331 encoded by ORF 1 a and/or the amino acid in position 946 encoded by ORF 1 b and/or the amino acid in position 10 encoded by ORF 2 is/are deleted.
 5. A nucleotide sequence coding for a virus according to any one of claims 1 to
 4. 6. The nucleotide sequence according to claim 5, wherein the nucleotide sequence has been modified to encode a virulence marker and/or a serological marker.
 7. The nucleotide sequence according to claim 6, wherein the nucleic acid encoding said marker is located within any of the open reading frames encoding structural viral proteins.
 8. A method for the generation of an infectious live attenuated PRRS virus comprising producing a recombinant nucleic acid comprising at least one full-length DNA copy or in vitro-transcribed RNA copy or a derivative of either wherein said nucleotide sequence is a nucleotide sequence according to claim
 5. 9. A method for the generation of an infectious live attenuated PRRS virus comprising producing a recombinant nucleic acid comprising at least one full-length DNA copy or in vitro-transcribed RNA copy or a derivative of either wherein said nucleotide sequence is a nucleotide sequence according to claim
 6. 10. The method according to claim 8, comprising specifically mutating the nucleotide sequence corresponding to the nucleotide sequence encoding amino acid positions 321 to 341 of ORF 1 a and/or the nucleotide sequence corresponding to the nucleotide sequence encoding amino acid positions 936 to 956 of ORF 1 b and/or the nucleotide sequence corresponding to the nucleotide sequence encoding amino acid positions 1 to 20 of ORF 2 wherein at least one nucleotide at said positions is substituted or deleted.
 11. The method according to claim 9, comprising specifically mutating the nucleotide sequence corresponding to the nucleotide sequence encoding amino acid positions 321 to 341 of ORF 1 a and/or the nucleotide sequence corresponding to the nucleotide sequence encoding amino acid positions 936 to 956 of ORF 1 b and/or the nucleotide sequence corresponding to the nucleotide sequence encoding amino acid positions 1 to 20 of ORF 2 wherein at least one nucleotide at said positions is substituted or deleted
 12. A pharmaceutical composition comprising a PRRS virus according to any one of claims 1 to 4; and a pharmaceutically acceptable carrier.
 13. A method for the prophylaxis and treatment of PRRS infections comprising administering a PRRS virus according to any one of claims 1 to
 4. 